Vaccination of yearling horses against poly-N-acetyl glucosamine fails to protect against infection with Streptococcus equi subspecies equi.
Authors: Cohen Noah D, Cywes-Bentley Colette, Kahn Susanne M, Bordin Angela I, Bray Jocelyne M, Wehmeyer S Garrett, Pier Gerald B
Journal: PloS one
Summary
# Editorial Summary Strangles remains endemic in equine populations worldwide, and whilst commercial vaccines exist, their efficacy and safety profiles remain problematic, prompting investigation into alternative immunogenic targets. Researchers vaccinated yearling horses using intramuscular injection alone or combined intramuscular and intranasal administration of poly-N-acetyl glucosamine (PNAG), a surface antigen expressed by *Streptococcus equi* subspecies *equi*, then exposed vaccinated and control animals to naturally infected horses in a controlled experimental setting. Although vaccinated horses generated functional antibodies capable of complement deposition and opsonophagocytic killing of the bacterium *in vitro*, neither vaccination strategy provided protection against clinical infection when challenged with live pathogen. The findings suggest that targeting PNAG alone is insufficient for effective strangles prevention, and that successful vaccine development will likely require inclusion of additional antigenic components—particularly those targeting bacterial enzymes capable of degrading or neutralising equine IgG—to overcome the pathogen's immunoevasion mechanisms. This work highlights the complexity of generating durable immunity against strangles and underscores the need for multi-component vaccine strategies rather than reliance on single surface antigens.
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Practical Takeaways
- •Existing commercial strangles vaccines have documented limitations; this study suggests that PNAG-based approaches alone do not provide adequate field protection even when generating measurable immune responses
- •When managing strangles vaccination programs, practitioners should recognize that in vitro antibody functionality does not guarantee in vivo protection, and contact exposure remains a significant infection risk
- •Future vaccine development should focus on multi-component strategies targeting SEE's immune evasion mechanisms, not single antigens alone
Key Findings
- •Vaccination with poly-N-acetyl glucosamine (PNAG) antigen generated functional antibodies that mediated complement deposition and opsonophagocytic killing of SEE in vitro
- •Both intramuscular alone and combined intramuscular plus intranasal immunization strategies targeting PNAG failed to protect yearling horses against experimental SEE infection following contact exposure
- •Current PNAG-based vaccine approach is insufficient for clinical protection and may require additional antigenic components targeting SEE virulence factors